The present invention generally relates to image processing systems, and more particularly, to image processing systems used to control vehicle equipment, such as vehicle headlamps, windshield wipers, etc.
Recently, many vehicular control accessories utilizing image processing systems have been proposed. For example, U.S. Pat. No. 5,837,994 entitled “Control System to Automatically Dim Vehicle Head Lamps,” commonly assigned with the present invention and hereby incorporated by reference, discloses a control system which utilizes an image sensor and a processor to detect the headlamps of other vehicles at night and automatically control the state of the high beam headlamps of a vehicle. Another example of an image processing system to control vehicle equipment is given in U.S. Pat. No. 5,923,027 entitled “Moisture Sensor and Windshield Fog Detector,” also commonly assigned with the present invention and hereby incorporated by reference. This patent discloses an image processing system, which acquires images of a vehicle windshield in order to detect the presence of rain or fog.
In each of these systems, as well as several other disclosed automotive image processing systems (see, for example, U.S. Pat. Nos. 5,765,116, 5,675,489, and 5,660,454 and PCT Published Patent Application No. WO 00/53465), images are acquired by an image sensor and stored into a memory in their entirety for subsequent processing. While technically very convenient, the use of this amount of image memory presents problems when adapting the system for commercial use, especially in the highly cost-sensitive automotive market. Most low cost microcontrollers or digital signal processors (DSPs) suitable for these types of applications are equipped with only a few hundred bytes to a few kilobytes of random access memory (RAM) into which the images can be stored. The processing core of many microcontrollers is typically available with a variety of RAM configurations, with the price increasing as the amount of memory increases. Therefore, it is advantageous to use a microcontroller with the least amount of RAM possible. The use of a small amount of RAM in prior art systems limits the size of the image, which can be stored and thus greatly limits the resolution.
A common off-the-shelf image sensor may have 352×288 pixels, known as the CIF format. Storing an entire image from this sensor requires approximately 100 kilobytes of RAM—far more than is typically available on a low cost microcontroller. Some microcontrollers have the ability to increase the amount of RAM available by the addition of an external memory chip. These microcontrollers must have an external memory bus, increasing the pin count and thus the cost and complexity of the microcontroller and the circuit board to which it is attached. The cost of the external memory itself must also be considered, and despite rapid memory price declines, this cost is anticipated to remain significant for some time to come. Finally, if an image must be transferred to memory before it can be processed, the total time required to acquire and analyze an image will be greater than if the analysis could occur simultaneously with the acquisition.
What is needed is a low cost image processing system to control automotive equipment which is capable of analyzing images without first storing them to memory, thus reducing the total amount of memory required in the system.